Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention is directed to tools and methods of producing and treating them. More particularly, the present invention is directed to tools that are treated by modifying at least a region on at least one surface of the tool by texturing the region in order to, for example, improve the retention capability of the tool in a tool holder. The tool may be, for example, a cutting tool insert or a chip breaker. The present invention also relates to methods of producing or treating a tool. Thus, the methods of the present invention may be applied in the production or treatment of cutting tools, and a particular application of the present methods is in the production of cutting tool inserts and/or chip breakers used in the machining of metals and other materials.
2. Description of the Invention Background
Castings, forgings, or other metal-containing preforms often are subjected to machining so as to convert the preform into a final product of the desired shape, size and/or finish. Machining is generally defined as the process of removing unwanted material from a workpiece. In a common form of a machining process known as chip machining, a surface of a cutting tool is brought into forceful contact with a workpiece and separates material from the workpiece in the form of small chips. The cutting tool may include a tool holder having a shank that can be mounted on a machine tool. A cutting tool insert formed of a high strength, high hardness material is removably secured on the tool holder, and the cutting tool insert can be replaced once worn. During the machining process, it is important that the cutting tool insert be securely seated and retained in a fixed position within the tool holder. Even slight movement of the cutting tool insert during the machining process can result in failure of the insert or production of material that is outside the desired tolerance specifications. Most manufactured products contain one or more components manufactured by machining, and often the machining step or steps produce the components to very precise tolerances. Machining, while one of the most basic and important processes used in manufacturing metal products, also is one of the more expensive. Thus, even modest improvements in the machining process may yield substantial cost savings.
There are a number of basic chip machining processes, including turning, boring, shaping, milling, drilling, sawing, and broaching. In one such process, turning, external surfaces of revolution may be generated by the action of a cutting tool insert on a rotating workpiece. Typically, the workpiece is mounted and rotated on a lathe. In turning, as in each of the other chip machining processes, the design of the cutting tool is critical to the efficiency by which material can be removed from the workpiece. Thus, substantial sums are spent each year to research and develop improved cutting tools for machining.
Cutting tool materials predominantly in use for production machining processes include high speed steels, carbides, cemented carbides (such as, for example, cemented tungsten carbide), cermets (carbide/ceramic), CBN (cubic boron nitride), PCD (polycrystalline diamond), and ceramics. Ceramics are preferred materials that are used commonly in cutting tool inserts used in turning operations. They are also one of the most recently developed classes of materials. Ceramics are particularly advantageous materials because they generally have high hardness, are relatively resistant to oxidation and, therefore, exhibit low tool wear at high cutting temperatures. The faster the cutting speeds, the higher the cutting temperature. Thus, the hardness, oxidation and wear resistance properties of ceramics allow ceramic cutting tools to be used with fast cutting speeds while maintaining long tool life, thereby improving the efficiency of the machining process.
Current ceramic materials used to produce cutting tool inserts are commonly based on either alumina (Al2O3) or silicon nitride (Si3N4). The production of ceramic articles generally, and ceramic cutting tool inserts in particular, involves the consolidation and sintering of powdered material. There are two basic methods of producing ceramic articles, cold pressing and hot pressing. In cold pressing, the powdered material is first consolidated, or pressed, into a green (unsintered) body. The green body is then sintered by heating the body to a high temperature below the melting point of the powdered material. The body is maintained at the high temperature for a time sufficient to fuse the powder particles and sufficiently densify the green body. In hot pressing, the powdered material is heated in a die while a high uniaxial pressure is applied to the body. Hot pressed ceramic usually has a finer grain size and higher density than cold pressed ceramic, thereby resulting in superior hardness and longer tool life.
Although ceramic cutting tool inserts made from hot pressed ceramic have properties superior to those made from cold pressed ceramic, cold pressed ceramic inserts are commonly used. One reason for the continued use of cold pressed ceramic cutting tool inserts is that forming ceramic by cold pressing arguably provides a greater degree of flexibility in designing the exterior contour of the inserts.
Some means is necessary to retain the cutting tool insert on the tool holder. Historically, cutting tool inserts formed by hot or cold pressing were designed with a bore therethrough, as shown in FIG. 4(a). In this design, the cutting tool insert 130 is secured in the pocket 126 of the tool holder 120 by inserting and threadedly securing a locking pin 150 through the bore 132 and into a bore 124 in the tool holder 120. Because a large volume of material is removed from a central region of the cutting tool insert 130 to provide bore 132, the strength of the insert may be reduced.
In an alternative design, the cutting tool insert is retained on the tool holder by a clamp. An example of this design is shown in FIG. 4(b). A generally L-shaped clamp 240 secures the cutting tool insert 230 to the tool holder 120. One leg 246 of the L-shaped clamp 240 is secured within bore 122 of the tool holder 120, while the other leg 248 is disposed against an exposed flat face 232 of the cutting tool insert 230. Cutting tool inserts composed of either hot or cold pressed ceramic may be used in this cutting tool design. Because the cutting tool insert 230 of FIG. 4(b) lacks a central bore, the strength of the insert is not compromised. On the other hand, the insert 230 of the design of FIG. 4(b) is not, in general, secured to its tool holder as strongly as the insert 130 of FIG. 4(a).
Another prior art cutting tool design is shown in FIG. 4(c). Here, the cutting tool insert 330 includes a depression 332 in at least one surface 334. One leg 346 of a generally L-shaped clamp 340 is secured within bore 122 of the tool holder 120 while the other clamp leg 348 is seated in the depression 332. As will be apparent to those skilled in the art, there are many different conventional designs of L-shaped clamp 340. This arrangement more positively secures the insert 330 in the pocket 126 of the tool holder 120 relative to the arrangement of FIG. 4(b). Hot pressing cannot be economically applied readily to produce cutting tool inserts having a depression as shown in FIG. 4(c).
Accordingly, there exists a need for an improved arrangement for securely retaining cutting tool inserts on tool holders. Preferably, the improved retention arrangement may be used with both hot pressed and cold pressed inserts and will not adversely affect the strength properties of the inserts.
The present invention provides a tool and a method of treating a tool for material removal. The tool is produced by a method that includes texturing at least one region of a surface of the tool so that the surface roughness of the region is greater than the surface roughness of untextured surfaces of the tool and wherein the textured region is spaced away from a cutting edge of the tool. The textured region may be used, for example, to improve the retention capability of the tool in a tool holder. Preferably, the textured region has an arithmetic average surface roughness, Ra, of greater than 30 xcexcin. The tool may, for example, be a cutting tool insert or a chip breaker.
The texturing treatment of the present invention results in an increase in the friction resistance of the tool, as measured by a xe2x80x9cpush blockxe2x80x9d test described below, to an amount greater than 5 in-lb. This represents the maximum friction resistance measured by the present inventors for a conventional ground ceramic cutting tool insert having generally planar surfaces not treated by the method of the present invention.
The present invention also is directed to a method of removing material from an article by machining the article with a tool, wherein the tool is provided by a method comprising texturing at least one region of at least one surface of the tool so that the textured region has a surface roughness that is greater than the surface roughness of untextured surfaces of the tool. The textured region is spaced away from a cutting edge of the tool. Preferably, the textured region has an Ra of greater than 30 xcexcin and the tool has a friction resistance of greater than 5 in-lbs.
The textured region may be produced by any of a variety of methods. A preferred method includes laser beam impacting the region. The textured region, however, may also be formed by other techniques including chemical and/or mechanical techniques such as grinding and sandblasting, molding, chemical etching, photolithography, and reactive ion etching. Other techniques will be apparent to those of ordinary skill upon considering the present description of the invention. One or more of these techniques are employed in the present invention to texture the treated region(s) of the article, thereby resulting in a surface roughness of the textured region(s) that is greater than the surface roughness of untextured surfaces of the tool. The textured region may be used to improve the retention of the tool in a tool holder. Preferably, the surface roughness of the textured region is greater than 30 xcexcin. The same texturing process also preferably increases friction resistance to greater than 5 in-lbs. The tool of the present invention may take the form of any tool with a cutting edge and at least one surface having at least one textured region that may be positioned and adapted to provide improved retention when secured to a toolholder. In such tools, the textured region is spaced away from the cutting edge. Such tools may include, for example, material removal tools such as a ceramic cutting tool insert that may be incorporated into a cutting tool system.
The present invention is also directed to a cutting tool system and a method of preparing the same, wherein the system includes a tool holder and a cutting tool insert having at least one surface having a textured region with Rathat is greater than 30 xcexcin (and preferably at least 63 xcexcin) and friction resistance greater than 5 in-lbs, and wherein the cutting insert is selectively securable to the tool holder. A cutting tool insert constructed according to the present invention can be used with standard prior art cutting insert clamps and tool holders without modifying the cutting tool, yet the amount of force required to dislodge the cutting tool insert is greater than that of a cutting tool insert that has not undergone the texturing process of the present invention. It is believed the increased surface roughness brought about by the texturing treatment of the present invention results in greater friction resistance between the cutting tool insert and the cutting insert clamp. The cutting insert clamp is composed of a material that is softer than the material comprising the face of the insert in contact with the clamp. After the cutting insert clamp is tightened onto the textured region of a cutting insert constructed according to the present invention, the clamp surface in contact with the textured region deforms such that displacement of the cutting tool insert out of the tool holder pocket and relative to the clamp can occur only after the clamp surface is sheared and plastically deforms.